Maintained by Robin Tecon, microbiologist and postdoctoral researcher at the Swiss Federal Institute of Technology Zürich. This blog is about bacteria (and other microbes) and the scientists who study them.

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Sunday, July 15, 2012

Are all our modern health issues linked to our microbiome?

The human microbiome is definitely the sensation of this Summer
2012. [Kind
of a Carly Rae Jepsen for science!]

In June alone, our microbial inhabitants were featured
on the cover of Scientific American
(watch their beautiful infographics), Nature,
Science and Microbe…

The Human Microbiome Project (HMP), a $170 million research consortium
funded by the US National Institute of Health (NIH), just released two reports
in Nature accompanied by fifteen
publications in PLoS ONE. The
consortium, strong of about 200 researchers, studied the diversity of microbes
inhabiting the body (skin, mouth, nose, gut, urogenital tract) of 242 healthy
people, using new sequencing technologies to catalog the microbes.

The bottom
line? Microbial diversity is very high between healthy individuals. It is
therefore impossible to define a typical ‘healthy’ microbiome. In a way, every
individual develops his/her own personal set of microbes. The diversity, however, is
not totally random and patterns are clearly present in various areas of the
body.

The amount of sequence data produced by HMP is almost overwhelming:
1000 times more than for the Human Genome Project! No doubt there is still a
tremendous amount of information to mine in this dataset. And HMP is not the
only project out there. Metagenomics of the Human Intestinal Tract (MetaHIT) is
a European-funded project that released its results last year. Both programs
are ending this year and are now looking for a follow-up, as Michael Balter
clearly explains in a Science News article.
Balter writes:

“One big question for the future is whether to stress gathering
more data on healthy and unhealthy microbiomes or focus on establishing causal
relationships between the microbiome and disease.”

I think this is the crux of the matter. Can we go beyond
correlation of microbial diversity with illness, and show some causal effects?
This is essential since many studies suggest a role of the microbiome in
crucial aspects of our health.

Obesity, for instance, is repeatedly pointed at. Helicobacter pylori, the ulcer-causing
bacterium, has now been shown to help regulate the production of ghrelin, a
human hormone that controls food intake, and therefore reduce weight gain—this
is the work of Martin Blaser at New York University. More and more children, Blaser
warns, grow without H. pylori in
their stomach. Is it enough to explain the epidemy of obesity? Probably not,
but this may not be trivial at all.

Bacteria may not be the only microbes influencing obesity.
The Adenovirus 36 (Adv36), which infects humans, has the power to modify its
host physiology (Atkinson, 2012). Indeed,
obesity correlates with Adv36 infection in adults, and even more in children.
As Atkinson rightly writes in his article:

“Having an infectious agent
responsible for obesity forces all of us to reconsider this condition, which is
widely held to be self-inflicted through inappropriate diet and activity
levels.”

So, who are we to blame? Bacteria, viruses, our dietary habits?
Most probably there is no single culprit, but the realization that our microbes
matter so much is revolutionary.

Immunity is another issue of tremendous importance. Here as
well, evidence is piling up to suggest that commensal microbes actively participate in
the building of a healthy human immune system (Olszak, 2012). And just as for
obesity, autoimmune disorders (for instance asthma) are on the rise in our
modern society. Our beneficial microbiome is globally in decline, due to an
increase in hygiene standards and the common use of antibiotics (two things, it
has to be noted, that are intrinsically good and save millions of lives every
year).

The ‘microbiota hypothesis’, proposed by Sarkis Mazmanian from Caltech,
suggests that the lack of exposure to commensals is triggering the increase in
allergic disease. This view is shared by Martin Blaser, who showed that H.
pylori can also protect against asthma. Blaser writes in his abstract (Blaser, 2012):

“The phenomenon of
disappearing ancient microbiota may be a general paradigm driving the diseases
of modernity.”

So, back to the title question: are all our modern health
issues linked to our microbiome? I suppose the answer is the classical scientific
answer: Maybe, but it’s complicated and we don’t understand the whole story yet.

But definitely a strong light now shines on the human
microbiome and its role in our health and well-being.